This invention relates generally to the detection of parenterally transmitted diseases and their detection, and more particularly, relates to Trypanosoma cruzi which is the causative agent of Chagas' Disease, and assays for its detection in test samples.
The protozoan parasite Trypanosoma cruzi is the causative agent responsible for a disease known as Chagas' Disease or as American Trypanosomiasis. The geographical range of this disease in the Americas is as far north as California and Maryland and as far south as regions in Argentina and Chile. It has been estimated that 90 million people are at risk, and that an additional 12 to 63 million individuals are infected with this parasite. See, for example, G. A. Schmunis, Transfusion 31:547-557 (1991); Anonymous, WHO Technical Report Series 1991 811:1-93 (1991); and S. Kingman, New Scientist 132:16-17 (1991). The first indigenous case of Chagas' Disease in North America was reported in 1955. N. C. Woody et al., JAMA 159:676-677 (1955); R. J. Schiffler et al., JAMA 251:2983-84 (1984); J. D. Pearlman, Am. J. Med. 75:1057-1060 (1983); T. R. Navin, Am. J. Public Health 75:366-369 (1985); and Anonymous, Texas Health Bull. 159:11-13 (1955).
Chagas' Disease is transmissable through blood products; the transmission of Chagas' Disease through blood transfusion in the United States has been recognized for some time. Two recent serological surveys in the Washington, D.C. area have indicated that several individuals residing in that area, originally from El Salvador and Nicaragua, had sera reactive for Chagas' Disease. L. V. Kirchhoff et al., JAMA 254:3058-3060 (1985); and L. V. Kirchhoff et al., Am. J. Med. 82:915-920 (1987). It has been estimated from this survey that there are up to 100,000 individuals living in the United States who are chronically infected with T. cruzi. A. Skolnick, JAMA 265:173 (1991). In a separate report, of 1027 consecutive blood donations in Los Angeles County during a three-month period which were screened by a complement fixation test for Chagas' Disease, there were ten initial reactives and one confirmed case. P. Kerndt et al., Transfusion 28:31S Abstract s108 (1988) and P. Kerndt et al., Transfusion 31:814-818 (1991). Imported Chagas' Disease has been recognized in Europe as well, with a documented case of congenital T. cruzi infection reported in Sweden. P. O. Pehrson et al, Scand. J. Infect. Dis. 13:307-308 (1981).
Trypanosoma cruzi has one of the most complex life cycles of trypanosomes found in man. Trypomastigotes circulate in the blood of vertebrate hosts and are transmitted by blood-sucking triatomid insects. The disease also can be spread by blood transfusion, through intravenous drug use, by congenital transmission, by sexual activity, by organ transplant or through breast milk. See, for example, A. Skolnick, JAMA 262:1433 (1989); P. Nickerson et al., Ann. Intern. Med. 111:851-853 (1989); Anonymous, Clinica 354:16 (1989); L. V. Kirchhoff, Ann. Intern. Med. 111:773-775 (1989); G. Bonfim et al., ISBT/AABB Joint Congress, Abstract S445, 112 (Nov. 10-15, 1990); P. Kerndt et al., Transfusion 28:S108 (1988); I. H. Grant et al., Ann. Intern. Med. 111:849-851 (1989); M. Boxaca et al., Int Conf. AIDS 6:437 (Abstract 3141) (1991); S. G. Sandler, Am. Red Cross Blood Services Letters 89:1-10 (1989); A. L. Bittencourt, Am. J. Dis. Child 130:97-103 (1976); R. Hoff et al., Trans. R. Soc. Trop. Med. Hyg. 72:247-250 (1978); M. D. Gudino et al., in Emerging Global Patterns in Transfusion-Transmitted Infections, R. G. Westphal et al., eds., Arlington, Va., American Association of Blood Banks, 65-86 (1990); I. G. Kagan et al., Rev. Biol. Trop. 14:55-73 (1966); I. C. P. Dias et al., Mem. Inst. Oswaldo Cruz 79:139-147 (1984); and J. H. Maguire et al., "American Trypanosomiasis" in Infectious Diseases, P. D. Hoepricke et al., eds, Philadelphia: J. P. Lippincott, pp. 1257-1266 (1989).
Diagnosis of the disease commonly is accomplished by identification of parasites in the blood, cerebrospinal fluid, fixed tissue or lymph node during periods of high fever; however, the organisms may be difficult to detect during the latent (or so-called indeterminant) phase, or during chronic stages of infection. In xenodiagnosis, the intestinal contents of insect vectors are examined for T. cruzi several weeks after these parasites feed on the blood of a suspected patient. However, this procedure is laborious and lacks sensitivity. E. L. Segura, "Xenodiagnosis" in Chagas' Disease Vectors, R. R. Brenner et al., eds., 11:41-45, Boca Raton, Fla., CRC Press (1987)
Several different serologic methodologies have been used to diagnose Chagas' Disease. These methodologies include indirect immunofluorescence, indirect hemagglutination, complement fixation and enzyme immunoassay. See, for example, F. Zicker et al., Bull. World Health Organ. 68:465-471 (1990); M. E. Carmargo, Rev. Inst. Med. Trop. Sao Paulo 8:227-234 (1977); M. E. Carmargo et al., Bull. Pan Am. Health Organ 19:233-264 (1985); A. A. Pan et al., J. Infect. Dis. (165:585-588 [1992]); A. A. Pan et al., Am. J. Trop. Med. Hyg. 45:120 Abstract 66 (1991); A. F. Ferreira et al., Rev. Inst. Med. Trop. San Paulo 33:123-128 (1991). Specific antibody responses to the parasite are detectable after infection, and the titers typically remain high for life. D. M. Israelski et al., Am. J. Trop. Med. Hyg. 39:445-455 (1988); R. Lelchuck et al., Clin. Exp. Immunol. 6:547-555 (1970); N. H. Vattuone et al., Am. J. Trop. Med. Hyg. 76:45-47 (1973).
The natural transmission of Chagas' Disease in humans occurs when skin or mucosa come in contact with feces of infected bugs. The signs and symptoms are so mild that the recent infection usually is not associated with T. cruzi infection. Even without treatment, the majority of individuals recover from the acute stages of disease. After a latent period of years or decades, a percentage of individuals (20-40%) develop the cardiac or gastrointestinal symptoms that characterize chronic Chagas' Disease. Persistence of parasitemia in asymptomatic individuals and survival of the parasite in banked blood and blood components increases the dangers of transmission of Chagas' Disease by blood transmision; infected blood used for transfusion in blood banks poses a significant public health problem. A rapid and reliable assay with standardized components for screening and confirming blood donors for Chagas' Disease thus would be extremely useful in preventing transfusion of the disease by blood banks.